JP2000332691A - Optical output control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical output control circuit by which the strength of a light signal is easily and fixedly kept and also various kinds of additional functions are provided. SOLUTION: A light quantity detecting circuit part 9 includes an optic/electric conversion circuit 6 and an ADD converting circuit 7 for digitally converting the level of an analog voltage outputted from the circuit 6. An attenuator control circuit 5 gives an attenuation amount corresponding to the value of a digital control signal from a CPU 4 to a variable light attenuator 2. Relation between a digital value outputted from the part 9 and an output optical signal strength(output level) and the relation between the value of the digital control signal and the attenuation amount of the attenuator 2 are previously set in a relative table 8. The CPU 4 decides the attenuation amount in the attenuator 2 by the digital signal so that the output level is set to the desired value by one-time control without the necessity of several-time fine adjustment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical output control circuit for maintaining the intensity of an optical signal at a desired value.

[0002]

2. Description of the Related Art In order to set the intensity of an optical signal sent to an optical fiber to a constant value, an optical output control circuit for maintaining the intensity of the optical signal at a constant value is used. The optical output control circuit is also used when the input optical signal is supplied to an optical module whose reception level is limited, for example, when the intensity of the input light is reduced to a certain level.

FIG. 9 is a block diagram showing a configuration of a conventional light output control circuit. Light output control circuit 200 shown in FIG.
Sets the intensity of the optical signal input from the optical fiber 201 to a predetermined value, and then outputs the signal to the optical fiber 207. In the optical output control circuit 200, the input optical signal is input to the optical branching unit 203 through the variable optical attenuator 202. The optical branching unit 203 branches the input optical signal and
And input to the photoelectric conversion circuit 206.

[0004] The optical-electrical conversion circuit 206 converts an input optical signal as monitor light into an analog electric signal. The intensity of the monitor light and the amplitude of the analog electric signal are correlated. The analog electric signal is output to the attenuator control circuit 20.
5 is input. The attenuator control circuit 205 creates a control signal that specifies the amount of attenuation of the variable optical attenuator 202 according to the amplitude level of the analog electric signal, and outputs the control signal to the variable optical attenuator 202. The variable optical attenuator 202 sets the amount of attenuation according to the control signal.

[0005] The attenuator control circuit 205 outputs a control signal indicating that the amount of attenuation is increased when the amplitude level of the analog electric signal is larger than a predetermined value, and outputs the control signal when the amplitude level of the analog electric signal is smaller than the predetermined value. A control signal indicating that the amount of attenuation is reduced is output. By such control, the intensity of the optical signal output to the optical fiber 207 is maintained at a predetermined value. Such an optical output control circuit is disclosed in, for example, JP-A-4-150324 and JP-A-10-336114.

[0006]

However, the conventional light output control circuit can perform constant light output control, but cannot perform any more extensive control. For example, the optical output control circuit itself creates a monitor signal relating to the intensity of the optical signal, but if there is a request to externally monitor the intensity of the output light, the conventional optical output control circuit meets the demand. It is not easy to respond. For example, the optical-electrical conversion circuit 206 that generates the monitor signal
In general, a photodiode (PD) is used, but since the input / output characteristics of the PD are not linear, an external P
Even if the output of D is observed, the intensity of the optical signal cannot be immediately recognized from the monitor signal. Further, since the characteristics of PDs vary, even if monitor signals from a plurality of optical output control circuits indicate the same analog voltage level, the intensity of the optical signals output from each optical output control circuit is the same. Is not always the case.

[0007] Japanese Patent Application Laid-Open No. 8-37499 discloses that
A control circuit for maintaining the intensity of an optical signal at a predetermined value by digital processing by a CPU is described. In the control circuit,
Contains a translation table. However, the control circuit is configured to obtain the attenuation amount according to the monitor level at that time from the conversion table, and to further confirm the output light intensity according to the obtained attenuation amount. Therefore, until the desired output light intensity is obtained, it is necessary to repeatedly check the light intensity while changing the attenuation amount by a small amount many times. In addition, the control circuit does not take into account any external signal monitoring or the like.

Accordingly, an object of the present invention is to provide an optical output control circuit capable of easily maintaining the intensity of an optical signal constant and providing various additional functions.

[0009]

According to the present invention, there is provided an optical output control circuit comprising: an A / D converter for converting a monitor signal for monitoring an output optical signal into a digital signal to generate a digital signal; A table is searched based on a table in which data for determining a variable corresponding to the value can be determined from the digital signal and the digital signal output by the A / D conversion means, and the output level of the optical signal matches the target value. And a data processing means for determining a variable amount for supply to the variable amount control means.

In the table, for example, the relationship between each digital signal and each output level and the relationship between each digital control signal and each variable amount in the level varying means are set.

The light output control circuit may include an interface for outputting the digital signal output from the A / D converter to the outside. The light output control circuit is, for example, a RAM. When an interface unit is provided, the output level can be monitored by an external device, and the target value can be easily changed from the external device.

In the table, correction data for correcting the output level may be set. The correction data includes, for example, data indicating the insertion loss for each wavelength in the optical multiplexer connected to the output side. Then, the data processing means may perform a process of adding an insertion loss according to the wavelength of the optical signal to be handled to the target value in order to correct the output level. When the correction data is included, it becomes possible to compensate for the insertion loss of each channel of the optical multiplexer to make the intensity of each wavelength in the multiplexed optical signal uniform.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of a light output control circuit according to the present invention. In the optical output control circuit 100 shown in FIG. 1, an optical signal input from the optical fiber 201 is input to the optical branching unit 3 through the variable optical attenuator 2. The optical branching unit 3 branches the input optical signal and inputs the optical signal to the optical fiber 207 and the light amount detection circuit unit 9.
The light amount detection circuit section 9 includes a light-to-electricity conversion circuit 6 and an A / D conversion circuit 7 for digitally converting the level of an analog voltage output from the light-to-electricity conversion circuit 6.

The A / D conversion circuit 7 is connected to the CPU 4 via a bus 20. The bus 20 is also connected with the attenuator control circuit 5, the correlation table 8, and the RAM 10. The attenuator control circuit 5 provides the variable optical attenuator 2 with an amount of attenuation according to the value of the digital control signal from the CPU 4. The correlation table 8 stores in advance the relationship between the digital value output from the light amount detection circuit unit 9 and the output optical signal intensity (output level), and the relationship between the value of the digital control signal and the attenuation of the variable optical attenuator 2. Is set. RA
M10 is, for example, a two-port RAM, which enables data exchange between the optical output control circuit and an external device.

FIG. 2 shows a table (A) showing the relationship between the digital value and the output level set in the correlation table 8, and
FIG. 4 is an explanatory diagram showing a configuration example of a table (B) showing a relationship between a digital control signal and an attenuation amount. Although each numerical value shown in FIG. 2 is merely an example value, in this example, the digital value-output level table sets digital values corresponding to each level in increments of 0.1 dBm. Also, the table of digital control signal-attenuation is set to 0.
An attenuation amount in 1 dB steps and a digital control signal designating each attenuation amount are set.

The relationship between the digital value and the output level is obtained, for example, by changing the input light signal intensity (input level) of the test light in a state where the attenuation of the variable optical attenuator 2 is set to 0, and detecting the corresponding light amount. It is determined by obtaining the output value of the circuit unit 9.

Here, the input level range of the test light is set wider than the input level range that can be input. The lower side of the test light input level range is
It is better to keep it wider. That is, the digital value-
In the output level table, the lower limit of the digital value is set to a value considerably lower than the level that can be handled. By doing so, when the digital value output from the light amount detection circuit section 9 indicates a value that is significantly lower than the level of the inputtable range, it can be determined that some trouble has occurred. Then, the CPU 4
The fact that a failure has occurred can be communicated to an external device via the RAM 10. The relationship between the digital control signal and the attenuation is determined based on the characteristics of the variable optical attenuator 2.

Next, the operation of the light output control circuit 100 will be described with reference to the flowchart of FIG. Note that the processing of steps S11 to S17 illustrated in FIG. 3 is executed at predetermined time intervals (for example, at one second intervals). Light output control circuit 1
At 00, the input optical signal is input to the optical branching unit 3 through the variable optical attenuator 2. The optical branching unit 3 branches the input optical signal and inputs the optical signal to the optical fiber 207 and the light amount detection circuit unit 9. In the light amount detection circuit section 9, the optical-electrical conversion circuit 6 converts an input optical signal as monitor light into an analog electric signal. The intensity of the monitor light and the amplitude of the analog electric signal are correlated. The AD conversion circuit 7
The level of the analog voltage output from the optical-electrical conversion circuit 6 is converted to digital. Then, the CPU 4 inputs a digital signal from the A / D conversion circuit 7 via the bus 20 (step S11).

The CPU 4 searches a digital value-output level table based on the input digital signal value, and extracts an output level corresponding to the digital signal value (step S12). Then, the output level of the dB expression is written in the RAM 10 (step S13). Note that the processes in steps S12 and S13 have no direct relationship with the output level constant control, but the output level can be easily monitored in an external device by setting the output level in the RAM 10 in dB.

Further, the CPU 4 obtains the difference between the set value (target value) and the output level corresponding to the value of the input digital signal (step S14), and determines the attenuation of the variable optical attenuator 2 (step S15). ). Here, the set value is a digital value corresponding to a desired output level. Then, a digital control signal corresponding to the obtained attenuation is determined using a digital control signal-attenuation table (step S16). Then, it outputs the determined digital control signal to the attenuator control circuit 5 via the bus 20.
The attenuator control circuit 5 controls the amount of attenuation of the variable optical attenuator 2 so that the variable optical attenuator 2 attenuates the input level with the amount of attenuation according to the digital control signal.

For example, it is assumed that the CPU 4 inputs "0100000000000" as a digital signal from the light amount detection circuit section 9. Referring to the digital value-output level table illustrated in FIG. 2, the output level corresponding to this value is +4 dBm. Here, the set value is 0 dBm
, The CPU 4 knows that the input level should be attenuated by 4 dB. Therefore, a digital control signal corresponding to the attenuation of 4 dB is obtained from the table of digital control signal-attenuation, and the digital control signal is output to the attenuator control circuit 5. The attenuator control circuit 5 controls the variable optical attenuator 2 so that the attenuation is 4 dB, so that the output level matches the set value.

In the above operation example, it is assumed that the attenuation of the variable optical attenuator 2 is 0 dB. However, if the attenuation of the variable optical attenuator 2 is already set to a value other than 0 dB, In the digital control signal determination processing of step S16, the CPU 4 sets a difference between the digital signal and the already-attenuated amount as a new amount of attenuation. For example, if the attenuation of the variable optical attenuator 2 is already 2 dB, and knows that the input level should be attenuated by 4 dB, the CPU 4 selects a digital control signal corresponding to the attenuation of 6 dB.

In this embodiment, the CPU 4 refers to a table based on digital values as monitor signals, and
A digital control signal for matching the output level to the set value is determined. The digital control signal is a variable optical attenuator 2
, The output level immediately matches the set value. That is, the output level can be made to match the set value by one control operation.

The optical output control circuit 100 shown in FIG. 1 attenuates the input level and outputs an optical signal having a constant output level. However, an optical signal having a constant output level higher than the input level can be output. In that case, as shown in FIG. 4, for example, an optical output control circuit 110 in which an optical amplifier 11 is installed at a stage subsequent to the variable optical attenuator 2 may be used. Even in such a configuration, the CP
U4 operates similarly to the case of the optical output control circuit 100 shown in FIG. 1, and can keep the output level of the optical signal constant.

FIG. 5 is a block diagram showing a configuration in which an external terminal 30 is connected to the light output control circuit 100. In this example, the terminal 30 is connected to the light output control circuit 100 via the RAM 10 having a two-port configuration. As described above, since the RAM 10 stores the value representing the output level of the optical signal in dB, the terminal 30 can immediately recognize the output level by reading the value from the RAM 10. For example, the terminal 30 has the RAM 10
To display the value on the display.

The terminal 30 can also provide a set value to the light output control circuit 100 via the RAM 10. In that case, the CPU 4 determines in step S14 that
The set value is read from the RAM 10, and a digital value corresponding to the read set value is used. Thus, the terminal 30
The setting value can be easily changed in accordance with the instruction from. In the configuration shown in FIG. 5, the light output control circuit 10
0 is illustrated, but the light output control circuit 11 shown in FIG.
0 can be connected to the terminal 30 similarly.

FIG. 6 is a block diagram showing an optical output control circuit according to the present invention using an OADM (Opt) for narrowband wavelength division multiplexing (NB-WDM) transmission.
ical Add Drop Multiplexe
1 is a configuration diagram showing a system configuration when applied to an r) system. The OADM system provides an optical signal of an arbitrary wavelength among n-wave WDM signals transmitted by WDM.
This is a system in which an optical signal can be extracted (dropped) or added (added) by an In-Line station (relay station), and is a system that can add value to the NB-WDM transmission system.

In the OADM system 300 shown in FIG.
Is a wavelength division multiplexed signal from the optical fiber 41,
(Demultiplexer) 12 for each wavelength λ₁, Λ₂, ...
・, Λ_nIs demultiplexed into signals of Each signal is a 2x2 optical switch.
Itch 13₁, 13₂, ..., 13_nIs input to
Each optical switch 13₁, 13₂, ..., 13_nsmell
An optical signal for Add is input to the other input.
You. In addition, each optical switch 13 ₁, 13₂, ..., 13
_n, One output is a light output control circuit
100₁, 100₂, ..., 100_nEntered in the other
The other output is taken out as a drop signal.

Light output control circuits 100 ₁ , 100 ₂ ,...
-, the structure of 100 _n may be the same as that of the light output control circuit 110 shown in optical output control circuit 100 or FIG. 4 shown in FIG. The light output control circuits 100 ₁ , 100 ₂ ,
..., the output of 100 _n may be multiplexed by the optical multiplexer (mux) 14 is output to the optical fiber 47.

In such a system, the optical switch 13 is controlled by the control unit 18 of the OADM system 300.
_{1, 13} 2, ..., through 13 _n, as or passes the optical signal of an arbitrary wavelength can be or replaced extraction.

The OADM system 300 has an external terminal
30 are connectable. The terminal 30 includes, for example, the control unit 18
Connected to. The control unit 18 includes a light output control circuit
100₁, 100₂, ..., 100_nRAM10
Can exchange data with each CPU 4
You. Therefore, the terminal 30 controls each optical output through the control unit 18.
Control circuit 100₁, 100₂, ..., 100_nOutput
You can monitor the level and give a set value.
Wear. The terminal 30 is connected to the light output control circuit 100 ₁, 10
0₂, ..., 100_nConnected to each of RAM10
It is good also as a structure which performs. Further, the control unit 18 controls each optical output.
Control circuit 100₁, 100₂, ..., 100_nCP
It is also possible to configure so as to bear the processing of U4.
You.

Generally, the multiplexer 14 has an insertion loss, but the insertion loss differs for each wavelength. In the WDM signal transmitted to the optical fiber 47, it is preferable that the intensity of each wavelength is uniform. However, if each of the optical output control circuits 100 ₁ , 100 ₂ ,..., 100 _n has the same output level, W
In the DM signal, the intensity of each wavelength varies.

Therefore, each optical output control circuit 100 ₁ , 10
0 _2, ..., a correlation table 8 of 100 _n, the correction table insertion loss of each channel (each wavelength) is set to store. FIG. 7 is an explanatory diagram illustrating an example of the correction table. As shown in FIG. 7, the correction table contains each wavelength λ.
The relationship between ₁ , λ ₂ ,..., Λ _n and the insertion loss is set. Note that each value shown in FIG. 7 is merely an example, and a value corresponding to the characteristics of the multiplexer 14 to be used is actually set.

FIG. 8 shows the CPU 4 using the correction table.
4 is a flowchart showing constant output control. In this case, the signal level sent to the optical fiber 47 is set as the set value. When a digital signal is input from the A / D conversion circuit 7 (step S11), the CPU 4 searches a digital value-output level table based on the input digital signal value, and outputs an output level corresponding to the digital signal value. Is extracted (step S12). Then, the output level of the dB expression is written in the RAM 10 (step S13).

In this case, the CPU 4 determines a correction value of the set value with reference to the correction table (step S2).
1). Then, the difference between the correction value and the output level corresponding to the value of the input digital signal is obtained (step S14).
The amount of attenuation of the variable optical attenuator 2 according to the difference is determined (step S15). Further, a digital control signal corresponding to the obtained attenuation is determined using a digital control signal-attenuation table (step S16), and the determined digital control signal is output to the attenuator control circuit 5 via the bus 20. I do.

For example, it is assumed that the set value, that is, the target value of the signal level transmitted to the optical fiber 47 is -20 dBm. Further, each optical output control circuit 100 ₁ , 100 ₂ ,.
..., the optical signal level, for example -1 is input to 100 _n
It is assumed that the variation is in the range of 2 dBm to -19 dBm. Assuming that the processing of step S21 is not performed, the processing of steps S11 to S17 (excluding S21) eliminates the variation of the input level of −12 dBm to −19 dBm, and the light output control circuits 100 ₁ , 100 ₂ ,.
-, 100 output level of the optical signal output from the _n is a value having a uniform, but would vary the light intensity of each wavelength in the WDM signal multiplexer 14 outputs.

[0037] However, in this case, the light output control circuit 100 ₁ for inputting an optical signal of wavelength lambda _1, the step S21
In the process ( ₁ ), it is known from the correction table that the insertion loss for the wavelength λ1 is 4.5 dB. Therefore, the correction value is set to -14.5 dB. Further, the light output control circuit 100 ₂ for inputting the optical signal of the wavelength lambda ₂ from the correction table, knowing that the insertion loss with respect to wavelength lambda ₁ is 5.0 dB. Therefore, the correction value is set to -15.0 dB. Then, each CPU 4 outputs a digital control signal to the attenuator control circuit 5 so that the output level matches the correction value.

Therefore, each light output control circuit 100 ₁ , 10
0 _2, ..., in the WDM signal from the multiplexer 14 for multiplexing the optical signals output from the 100 _n, the light intensity of each channel is assumed to uniform. As described above, each of the optical output control circuits 100 ₁ , 100 ₂ ,..., 100 _n
Performs constant output level control in consideration of the insertion loss of the multiplexer 14. In this case, each light output control circuit 10
_{0 1, 100 2, ···,} 100 n but is to output different levels of optical signals may their arrangement identical.

The signal level of each channel of the WDM signal input through the optical transmission path may vary. Further, there is a possibility that the level of the signal to be added varies. However, in this embodiment, the variation of the optical signal level can be eliminated by each of the optical output control circuits 100 ₁ , 100 ₂ ,..., 100 _n . Moreover, the signal level of each channel in the output WDM signal can be made uniform, and the possibility of a data error occurring on the receiving side can be reduced even if the WDM output signal is transmitted over a long distance.

It should be noted that also in this case, steps S12, S12
Since the output level is written to the RAM 10 in the process of step 13, the external terminal 30
_{1, 100} 2, ..., it is possible to immediately recognize the output level of optical signals from 100 _n. Therefore, even if a malfunction occurs among the light output control circuits 100 ₁ , 100 ₂ ,..., 100 _n , the terminal 30 immediately detects the malfunction. Further, setting values can be easily changed from the terminal 30.

In each of the above embodiments, the CPU 4 uses the digital signal as the monitor signal to determine the amount of attenuation in the variable optical attenuator 2 (not a relative amount for designating an increase or decrease in the amount of attenuation, but an amount of attenuation). Therefore, the output level is set to a desired value by one control without the need for fine adjustment many times. The output level is d
Since the data is written in the RAM 10 in the B expression, the RAM 1
0, the output level can be easily monitored by an external device. Further, it is easy to change the set value from an external device. The RAM 10 is an example of an interface unit, and data exchange with an external device can be realized by another interface unit.

Further, in addition to the functions realized in the above embodiments, various additional functions can be realized. For example, in addition to controlling the output level constant,
When a certain condition is met, complicated control such as shutting down the light output can be performed, and a wide range of light output control can be realized.

[0043]

As described above, according to the present invention, the optical output control circuit is provided with an A / D converter for digitally converting a monitor signal for monitoring an output optical signal to generate a digital signal, A table is set based on a table in which data for determining a variable amount corresponding to a target value of the output level from the digital signal is set, and a table is searched based on the digital signal output by the A / D conversion means to set the output level of the optical signal to the target. A data processing means for determining a variable amount to match the value and supplying it to the variable amount control means is provided, so that the intensity of the optical signal can be easily kept constant and various additional There is an effect that a function can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of a light output control circuit according to the present invention.

FIG. 2 shows a digital value set in a correlation table 8;
FIG. 4 is an explanatory diagram showing a configuration example of a table (A) showing a relationship between output levels and a table (B) showing a relationship between a digital control signal and an attenuation.

FIG. 3 is a flowchart showing an operation of the light output control circuit.

FIG. 4 is a block diagram illustrating another configuration example of the light output control circuit.

FIG. 5 is a block diagram showing a configuration in which an external terminal is connected to a light output control circuit.

FIG. 6 is a configuration diagram showing a system configuration when an optical output control circuit according to the present invention is applied to an OADM system for WDM transmission.

FIG. 7 is an explanatory diagram illustrating an example of a correction table.

FIG. 8 is a flowchart showing constant output control using a correction table.

FIG. 9 is a block diagram illustrating a configuration of a conventional light output control circuit.

[Explanation of symbols]

Reference Signs List 2 variable optical attenuator 3 optical branching unit 4 CPU 5 attenuator control circuit 6 optical-electrical conversion circuit 7 A / D conversion circuit 8 correlation table 9 light quantity detection circuit unit 10 RAM 11 optical amplifier 12 optical multiplexer (multiplexer) 13 ₁ , 13 ₂ ,..., 13 _n optical switch 14 optical demultiplexer (demultiplexer) 18 control unit 20 bus 30 terminal 41, 47 optical fiber 100, 110 optical output control circuit 100 ₁ , 100 ₂ ,. 100 _n optical output control circuit 201, 207 optical fiber 300 OADM system

Claims (7)

[Claims] A variable level means for varying an input level of an optical signal; a monitor means for monitoring an output level of the optical signal; and a variable means for controlling a variable amount of the level variable means in accordance with a monitor signal from the monitor means. An optical output control circuit comprising an amount control means; an A / D conversion means for converting a monitor signal into a digital signal to generate a digital signal; and a variable amount corresponding to a target value of an output level of the optical signal from the digital signal. A table in which data to be determined is set, and the table are searched based on the digital signal output by the A / D conversion means, and a variable amount for matching the output level of the optical signal with a target value is determined. And a data processing means for supplying the data to the variable amount control means. 2. The optical output control circuit according to claim 1, wherein a relation between each digital signal and each output level and a relation between each digital control signal and each variable amount in the level variable means are set in the table. . 3. The optical output control circuit according to claim 1, further comprising an interface for outputting a digital signal output from the A / D converter to the outside. 4. The light output control circuit according to claim 3, wherein the interface means is a RAM. 5. The light output control circuit according to claim 1, wherein correction data for correcting an output level is set in the table. 6. The optical output control circuit according to claim 5, wherein the correction data includes data indicating an insertion loss for each wavelength in an optical multiplexer connected to the output side. 7. The optical output control circuit according to claim 6, wherein the data processing means corrects the output level by performing a process of adding an insertion loss according to a wavelength of the optical signal to be handled to a target value.